(not applicable)
The invention relates generally to antennas, and more particularly to a drooping helix antenna able to provide excellent performance in a low profile configuration.
Helical antennas are well known in the art. See for example U.S. Pat. No. 5,541,617 issued Jul. 30, 1996, to Connolly et al.; U.S. Pat. No. 5,349,365 issued Sep. 20, 1994 to Ow et al.; U.S. Pat. No. 5,134,422 issued Jul. 28, 1992 to Auriol; U.S. Pat. No. 4,349,824 issued Sep. 14, 1982 to Harris; U.S. Pat. No. 5,255,005 issued Oct. 19, 1993 to Terret et al.; U.S. Pat. No. 5,170,176 issued Dec. 8, 1992 to Yasunaga et al.; and U.S. Pat. No. 5,198,831 issued Mar. 30, 1993 to Burrell et al., the teachings of which are hereby incorporated herein by reference. See also xe2x80x9cA Shape-Beam Antenna For Satellite Data Communicationxe2x80x9d published Oct. 12, 1976, by Randolph W. Bricker, Jr. AP-S Session 4, 1630, at the AP-S. International Symposium held in 1976 in Amherst, Mass., U.S.A., pp. 121-126. Drooping dipole antennas are also fairly well known as shown in U.S. Pat. No. 6,211,840, issued Apr. 3, 2001, to Wood et al and U.S. Pat. No. 4,686,536, issued August 1987, to Allcock, the teachings of which are hereby incorporated herein by reference.
As noted by Auriol, helical antennas offer the advantage of radiating an electromagnetic wave in a high-quality circular polarization state over a wide coverage area with a transmission lobe that may be shaped as needed for a given. application. These characteristics make helical antennas valuable in various fields of use, such as ground links with orbiting satellites or mobile/relay ground links with geosynchronous satellites.
Popular receiving helical antennas are typically either bifilar with two helices spaced equally and circumferentially on a cylinder or quadrifilar with four helices arranged the same way. Because of the radiation or coverage pattern thereof, quadrifilar helix antennas are typically well suited for mobile-to-satellite communication applications. As discussed in Antenna Engineering Handbook by Richard C. Johnson and Henry Jasik, pp. 13-19 through 13-21 (1984), a quadrifilar helix (or volute) antenna is a circularly polarized antenna having four orthogonal fractional-turn (one fourth to one turn) helixes excited in phase quadrature. Each helix is balun-fed at the top (although the helices can also be fed at the bottom) with four helical arms of wires or metallic strips of resonant lengths (l=.lambda./4, m=1, 2, 3, . . . ) wound on a small diameter with a large pitch angle. This antenna is a fairly well suited for various applications requiring a wide hemispherical or cardioid shaped radiation pattern. In addition, quadrifilar helix antennas generally offer a high bandwidth as compared to patch antennas over the high frequency ranges required for satellite communication (e.g., GPS) applications.
Recently, a need has been recognized for an antenna suitable for use in mobile satellite radio applications. For the reasons set forth above, the quadrifilar helix antenna is a prime candidate. One of the advantages of the quadrifilar antenna is its compact size and relatively small diameter. For the satellite radio application, the height of the antenna must conform to size and space constraints for a target environment (e.g. automobile installation). Unfortunately, as is well known in the art, the height of a quadrifilar helix antenna is directly related to its impedance. Consequently, any change in the height of the antenna will affect its impedance and its performance. Hence, changes in height of conventional quadrifilar helix antennas typically require a redesign of the impedance matching circuit associated therewith.
In addition, changes in the height of conventional quadrifilar helix antennas are limited in that the height of the antenna, that is, the length of the radiating elements, must be a discrete integer multiple of one quarter-wavelength (.lambda./4) of the operating frequency of antenna. Further such reductions in the height of conventional quadrifilar helix antennas are achieved, generally, at the cost of reduced gain.
In U.S. Pat. No. 6,229,499 issued May 8, 2001 to Licul, et al., assigned to the assignee of the present invention and incorporated herein by reference, a folded helical antenna is discussed offering the advantage of a low profile configuration and overcoming many of the detriments discussed above. As much as 20% height reduction can be achieved using such technique without degradation on antenna efficiency. Still, however, other alternative methods are needed that result in even lower-profile antennas (for example, 40 mm or less) to that provide adequate performance in a demanding target consumer market.
In a first aspect of the present invention, a drooping helix antenna comprises at least first and second radiating elements of conductive material, each element extending in a first direction in a first plane and having a portion thereof drooping in at least a second direction in a second plane. The drooping helix antenna further comprises means for individually feeding at least two of said elements and a means for maintaining said radiating elements in a substantially helical or spiral shape except for said drooping portion.
In a second aspect of the present invention, a drooping quadrifilar helix antenna comprises first, second, third, and fourth radiating elements of conductive material, each element extending in a first direction in a first plane and at least one of the radiating elements having a portion thereof drooping in a second direction in all, a second plane. The drooping quadrifilar helix antenna further comprises a dielectric tube for maintaining a substantial portion of said radiating elements in a substantially helical or spiral shape and a coupler for coupling electrical energy to and/or from each of said radiating elements, wherein said coupler includes a feed network for individually feeding at least two of said elements.
In a third aspect of the present invention, a drooping helix antenna, comprises a plurality of radiating elements each formed in a substantially parallel helical of spiral configuration, and a plurality of drooping elements (which also radiate) appended to a corresponding member of the plurality of radiating elements wherein at least a portion of each of the plurality of drooping elements are in substantial perpendicular relation to the corresponding member of the plurality of radiating elements.